attach more widgets to a QScrollArea

[franco.amato]

Hi to all,
I'm able to attach a widget to a scrollarea. I would know if it's possible to attach more than one qwidget to the same scrollarea.
So when I move the scrollbar, both widgets should be moved.

I tried with this code:

/* scroll area */
QScrollArea* sa = new QScrollArea( this );
sa->setWidgetResizable( true );
sa->setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
sa->setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOn );
 
QScrollBar *scrollBar = sa->horizontalScrollBar();
 
m_WaveDisplay = new WaveDisplay; //QWidget
m_TimeDisplay = new TimeWidget;    //QWidget
 
sa->setWidget(m_TimeDisplay);
sa->setWidget(m_WaveDisplay);
 
QVBoxLayout* layout = new QVBoxLayout();
layout->addWidget( sa );
 
..more code..

/* scroll area */
QScrollArea* sa = new QScrollArea( this );
sa->setWidgetResizable( true );
sa->setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
sa->setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOn );

QScrollBar *scrollBar = sa->horizontalScrollBar();

m_WaveDisplay = new WaveDisplay; //QWidget
m_TimeDisplay = new TimeWidget;    //QWidget

sa->setWidget(m_TimeDisplay);
sa->setWidget(m_WaveDisplay);

QVBoxLayout* layout = new QVBoxLayout();
layout->addWidget( sa );

..more code..

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but I get a crash when the application starts.
Maybe is not possible?

Best

[faldzip]

you can do it like this:

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

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[franco.amato]

you can do it like this:

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

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It works, thank you

[franco.amato]

you can do it like this:

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

QWidget w = new QWidget(this);
QVBoxLayout *lo = new QVBoxLayout;
lo->addWidget(m_TimeDisplay);
lo->addWidget(m_WaveDisplay);
w->setLayout(lo);
sa->setWidget(w);

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I spoken too early.
It doesn't work.
In the ctor of the m_TimeDisplay I have

setMinimumSize( QSize(800, 20) );
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed); // it must expand only orizzontally

setMinimumSize( QSize(800, 20) );
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed); // it must expand only orizzontally

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In the ctor of the m_WaveDisplay I have

setMinimumSize( QSize(800, 250) );
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed); // it must expand only orizzontally

setMinimumSize( QSize(800, 250) );
setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed); // it must expand only orizzontally

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Now in the ctor of the WaveWidget that must contains both m_TimeDisplay and m_WaveDisplay
I have the code you suggested to me:

/* scroll area */
QScrollArea* sa = new QScrollArea( this );
sa->setWidgetResizable( true );
sa->setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
sa->setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOn );
 
QScrollBar *scrollBar = sa->horizontalScrollBar();
 
QWidget* w = new QWidget();
w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1
 
QVBoxLayout* il = new QVBoxLayout;
il->addWidget( m_TimeDisplay );
il->addWidget( m_WaveDisplay );
w->setLayout(il);
sa->setWidget(w);
 
QVBoxLayout* layout = new QVBoxLayout();
 
layout->addWidget(sa);
layout->addLayout( infoLayout );
layout->addLayout(lo);
setLayout(layout);

/* scroll area */
QScrollArea* sa = new QScrollArea( this );
sa->setWidgetResizable( true );
sa->setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOff );
sa->setHorizontalScrollBarPolicy( Qt::ScrollBarAlwaysOn );

QScrollBar *scrollBar = sa->horizontalScrollBar();

QWidget* w = new QWidget();
w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1

QVBoxLayout* il = new QVBoxLayout;
il->addWidget( m_TimeDisplay );
il->addWidget( m_WaveDisplay );
w->setLayout(il);
sa->setWidget(w);

QVBoxLayout* layout = new QVBoxLayout();

layout->addWidget(sa);
layout->addLayout( infoLayout );
layout->addLayout(lo);
setLayout(layout);

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The result is in this image ( also attached )image.jpg
You can see that there are some not desired spaces and the widget w doesn't occupies all scrollarea surface.

I don't know where I'm wrong.

Best Regards,
Franco

[pezmaster31]

You can see that there are some not desired spaces

check out QBoxLayout::setSpacing()

the widget w doesn't occupies all scrollarea surface

check out QAbstractScrollArea::setViewportMargins()

[pezmaster31]

nevermind on my 2nd tip - QAbstractScrollArea::setViewportMargins() is protected

[wysota]

Add a spacer after the last widget and also play with setWidgetResizable().

[franco.amato]

check out QBoxLayout::setSpacing()

I set il->setSpacing(1) ans the above space is reduced to 1 pixel but I still have problems with the bottom space.
I'm trying all.
I'm sure the problem is in set the parents, in the logic.

check out QAbstractScrollArea::setViewportMargins()

I tried to call it but is protected and doc says that default values are 0 ( what I want, overall for the bottom space ).
The widget doesn't fit well the scroll area.
When I try to resize the widget ( with a zoom ) for an instant it fit all scroll area and then it come back to the previous size.
Something as a pulse.

Any idea?

[franco.amato]

Add a spacer after the last widget and also play with setWidgetResizable().

Hi,
how can add a spacer? I don't use designer. I played with setWidgetResizable but if I set it to false I can not zoom,
what I don't want.

Thank you

[wysota]

how can add a spacer?

QSpacerItem

I played with setWidgetResizable but if I set it to false I can not zoom,

I don't really know what you mean by "zoom" in this situation. In general this property should be set rather to true than to false (the latter is default).

[franco.amato]

QSpacerItem

I don't really know what you mean by "zoom" in this situation. In general this property should be set rather to true than to false (the latter is default).

Dear wysota in my case the m_TimeDisplay and m_WaveDisplay are used to show an audio wave were user can zoom in/out to navigate into the sound.
I would attach such widgets to a QScrollArea to leave to Qt manage when user zoom.

This is what I meant

[wysota]

That's not the way to go, really... Nevertheless, I don't see the problem. Would you care to explain?

[franco.amato]

That's not the way to go, really... Nevertheless, I don't see the problem. Would you care to explain?

Which is the way to go?

Well the problem is that the widget doesn't fit the scroll area.
I'm not sure the logic I used is correct ( assign the correct parent of every widget )

[pezmaster31]

Not sure if this is the ideal way to achieve this sort of behavior... but this seems to work on my end (if I understand you correctly)

// set size policy for your WaveDisplay widget to use as much vertical space on its parent as is available
m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
 
QVBoxLayout* il = new QVBoxLayout;
il->setSpacing(0);
il->addWidget(m_TimeDisplay);
il->addWidget(m_WaveDisplay);
 
QWidget* w = new QWidget();
// you had the widget's vertical size policy set to Fixed, so there's no way it could ever expand vertically, changed to Ignored (same as WaveDisplay)
// w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1
w->setLayout(il);
 
QScrollArea* sa = new QScrollArea;
sa->setWidgetResizable(true);
sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
sa->setWidget(w);

// set size policy for your WaveDisplay widget to use as much vertical space on its parent as is available
m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);

QVBoxLayout* il = new QVBoxLayout;
il->setSpacing(0);
il->addWidget(m_TimeDisplay);
il->addWidget(m_WaveDisplay);

QWidget* w = new QWidget();
// you had the widget's vertical size policy set to Fixed, so there's no way it could ever expand vertically, changed to Ignored (same as WaveDisplay)
// w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1
w->setLayout(il);

QScrollArea* sa = new QScrollArea;
sa->setWidgetResizable(true);
sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
sa->setWidget(w);

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[wysota]

Which is the way to go?

Either a completely custom widget derived from QAbstractScrollArea or Graphics View.

Well the problem is that the widget doesn't fit the scroll area.

setWidgetResizable(true) would fix the problem.

[franco.amato]

Either a completely custom widget derived from QAbstractScrollArea or Graphics View.


setWidgetResizable(true) would fix the problem.

Hi, I already set it to true. It doesn't solve the problem. I posted above the most important code. If you can give a look you can see that the setWidgetResizable(true) is set to true

[franco.amato]

Either a completely custom widget derived from QAbstractScrollArea or Graphics View.

I can rewrite it if it's the case. Can you give me some hints on how to do it? As now I inherited from QWidget.
I wrote WaveWidget : QWidget.
WaveWidget contains vertically aligned
1) TimeDisplay : QWidget
2) WaveDisplay : QWidget

I would attach a QScrollArea to WaveWidget as I said to allow user zoom without results

[franco.amato]

Not sure if this is the ideal way to achieve this sort of behavior... but this seems to work on my end (if I understand you correctly)

// set size policy for your WaveDisplay widget to use as much vertical space on its parent as is available
m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
 
QVBoxLayout* il = new QVBoxLayout;
il->setSpacing(0);
il->addWidget(m_TimeDisplay);
il->addWidget(m_WaveDisplay);
 
QWidget* w = new QWidget();
// you had the widget's vertical size policy set to Fixed, so there's no way it could ever expand vertically, changed to Ignored (same as WaveDisplay)
// w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1
w->setLayout(il);
 
QScrollArea* sa = new QScrollArea;
sa->setWidgetResizable(true);
sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
sa->setWidget(w);

// set size policy for your WaveDisplay widget to use as much vertical space on its parent as is available
m_WaveDisplay->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);

QVBoxLayout* il = new QVBoxLayout;
il->setSpacing(0);
il->addWidget(m_TimeDisplay);
il->addWidget(m_WaveDisplay);

QWidget* w = new QWidget();
// you had the widget's vertical size policy set to Fixed, so there's no way it could ever expand vertically, changed to Ignored (same as WaveDisplay)
// w->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
w->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Ignored);
w->setMinimumSize(800, 271); // 271 = 250(m_WaveDisplay) + 20(m_TimeDisplay) + 1
w->setLayout(il);

QScrollArea* sa = new QScrollArea;
sa->setWidgetResizable(true);
sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
sa->setWidget(w);

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Hi now the widget fit the scroill area but I still have some problems.
1) when I resize the widget ( for example user zoom in ) the widget seems to pulse. It grow and shrank (in the orizontally direction that must be fixed) continuosly every time user press zoom button
2) The scroll bar is not shown. The widget grow ( in a bad way ) but I can not navigate in it with the scroll bar.

May be my code of zoom is not correct.
This is the code

// executed when user press zoonin button
void WaveWidget::zoomIn()
{
	float f = m_ZoomFactor + 0.12;
	qDebug() << "WaveWidget::zoomIn - f: " << f;
	m_WaveDisplay->setZoomFactor( f );
}

// executed when user press zoonin button
void WaveWidget::zoomIn()
{
	float f = m_ZoomFactor + 0.12;
	qDebug() << "WaveWidget::zoomIn - f: " << f;
	m_WaveDisplay->setZoomFactor( f );
}

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And then the code to expand the WaveDisplay

/************************************************************************/
/* setZoomFactor                                                                                                                   */  
/************************************************************************/ 
void WaveDisplay::setZoomFactor( float f )
{
	int w, h;
 
	w = width() * f;
	h = height();
 
	setMinimumSize( w, h );
	QWidget* p = dynamic_cast<QWidget*>( parent() );
	if (p)
		resize( p->width(), p->height() );
	repaint();
}

/************************************************************************/
/* setZoomFactor                                                                                                                   */  
/************************************************************************/ 
void WaveDisplay::setZoomFactor( float f )
{
	int w, h;

	w = width() * f;
	h = height();

	setMinimumSize( w, h );
	QWidget* p = dynamic_cast<QWidget*>( parent() );
	if (p)
		resize( p->width(), p->height() );
	repaint();
}

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I'm sure my code is wrong but I don't know where...
The zoom is wrote in very few time and I'm not sure is a correct way to do it.
The code of the zoom of TimeDisplay is not implemented yet..

Regards

[franco.amato]

I changed the code of the zoom so:

/************************************************************************/
/* setZoomFactor                                                                                                                   */  
/************************************************************************/ 
void WaveDisplay::setZoomFactor( float f )
{
	int w, h;
 
	w = width() * f;
	h = height();
 
	setMinimumSize( w, h );
	QWidget* p = dynamic_cast<QWidget*>( parent() );
	if (p)
	{
		//resize( p->width(), p->height() );
		resize(w, h); // <--------------------------------------------------------CHANGED
	}
 
	repaint();
}

/************************************************************************/
/* setZoomFactor                                                                                                                   */  
/************************************************************************/ 
void WaveDisplay::setZoomFactor( float f )
{
	int w, h;

	w = width() * f;
	h = height();

	setMinimumSize( w, h );
	QWidget* p = dynamic_cast<QWidget*>( parent() );
	if (p)
	{
		//resize( p->width(), p->height() );
		resize(w, h); // <--------------------------------------------------------CHANGED
	}

	repaint();
}

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And now I don't get the "grow and shrank" effect when I zoom. But the status bar still doesn't appear.
I can not navigate into the wave.
Any idea?

Best

[wysota]

The zoom is wrote in very few time and I'm not sure is a correct way to do it.

Defintely not

You are artificially manipulating the size of each child widget which is not a very good idea. Using graphics view or implementing everything as one widget derived from QAbstractScrollArea would be a much better approach.